When an unvulcanized tire is to be molded by sticking a sheet member of unvulcanized rubber to a molding drum, the sheet member of the unvulcanized rubber is cut to a length for one tire, the cut sheet member is stuck to the molding drum, and then, the both end portions are joined or a plurality of sheet members are overlapped and joined on the respective side portions.
The joining is performed in general by pressing a roller against a joint end portion, by stretching joint surfaces to the end portions on the other side and by joining the both ends so that they overlap with each other (See PTLs 1 to 3). Furthermore, in addition to the above, PTL 1 also describes a device which presses swing claws forming a pair against a rubber sheet and contracts a relative distance of the outer edges, to thereby join the rubber sheet.
However, in the case where, for example, a sheet member of unvulcanized rubber handled by a large-sized (for OOR) single molding machine for molding a super-large tire is to be joined, the above-mentioned prior-art technology cannot be used for the following reasons, and a hand-zipper device of a member-clamping type using a bevel gear has been used so far:
That is,
(1) In the case of performing automatic joining, if a sheet member (ply) on the traveling direction side begins to open even slightly, the joining cannot be corrected in the middle and joining means such as, for example, a joining roll might idle and cannot join the sheet member well in some cases.
(2) In order to uniformly join the joint end portions, since the joining roll needs to be placed on the sheet member at a constant angle all the time, an inclined portion cannot be joined well in the case of the particularly large inclination of the sheet member.
(3) Since the vicinity of the end of the sheet member cannot be brought into close contact with a member on the lower side thereof for a folded ply wave measure, a joining device for pressing from above cannot be used.
In other words, in order to join the end portions of a ply having reinforcing cords embedded therein which is a sheet member of a super-large tire, a hand-zipper device operated manually has been used so far, and air is put into a bevel gear inside the hand-zipper device, that is, a rotation of the bevel gear is performed by an air motor, to thereby manually place the bevel gear on a ply joint end portion and to join the plies (sheet members).
However, the ply for the super-large tire is thick and also has a thick treat, and handling of the tire is hard work, and moreover, the prior-art hand-zipper device has a total weight of approximately 13 kg, which is too heavy to be held and operated by human, and when a worker performs joining ply having the reinforcing cords by the hand-zipper device, a quality of joined portion is varied, which is a problem.
Furthermore, when a clamping zipper is to be used, since the plies cannot be butted to each other as it is, a protrusion is made on the sheet member to be joined, but if the protrusion is made, a length of the ply exceeds the bonded periphery, and a work of manually holding down the extra portion is occurred after joining.
Therefore, automatic joining of the ply for the purpose of enhancement of productivity and alleviation of work load is required, but it is not easy to automate the work which has relied on human skills, and the hand-zipper devices have not been automated so far.